I have a 2014 infiniti qx60 hybrid. It has less than 50k miles. The past few months my car has been violently shaking upon acceleration, though it doesn't happen all the time, it'll usually happen after I've been driving a while or stuck in traffic. It'll shake when accelerating after being stopped, then I'll tap the gas a bit till it picks up speed and stop shaking when driving. It's under extended warranty, ive taken car to 2 dealerships several times, but the dealership can't find anything wrong with it so they say they can't do anything for me since their computer doesn't find any warnings. Please help.